This invention relates to a flow passage changeover valve assembly provided in a pipeline connecting an emergency water storage tank for use in emergency cases such as earthquakes with the water main for changing the course of water flow, and a four-port changeover valve and a three-way valve used in such a valve assembly.
Emergency water storage tanks are buried under roads, schoolyards, parks, etc. to supply water to neighboring residents or for fire-extinguishing purposes in the case of earthquakes and other disasters.
As shown in FIG. 14, such a tank T is connected to the water main S through inlet and outlet bypass lines P each provided with an emergency shutoff valve 1. An on-off valve 2 adapted to be opened in an emergency case is provided in the water main S between the bypass lines P. The tank T has a fireplug 3, a manual pump 4 and an air valve 5.
In a normal situation, the shutoff valves 1 are open and the on-off valve 2 is closed. Water thus flows as shown by arrows A-D to fill the tank and also to prevent rotting of water in the tank. In the case of an emergency such as an earthquake, the shutoff valve 1 is closed and the on-off valve 2 is opened to shut off the tank T from the water main S, thus preventing escape of water from the tank T due to the siphoning effect, while maintaining the water flow through the water main S.
A four-port butterfly valve having all the functions of the shutoff valves 1 and the on-off valve 2 is disclosed in unexamined Japanese utility model publication 6-59673 and unexamined Japanese patent publication 64-21275.
As shown in FIG. 15, such a butterfly valve v has its two ports connected to bypass lines P and the remaining two ports to the mains S. In a normal situation, its valve body 7 is positioned as shown by chain line to let water flow as shown by arrows A-D. In an emergency, the valve body 7 is moved to the position shown by solid line to shut off the bypass line P from the water main S.
The arrangement in which two shutoff valves 1 and one on-off valve 2, a total of three valves, are used is not only uneconomical but also its maintenance is troublesome. The three valves tend to fail more frequently and thus is less reliable than a single valve. Further, operating the three valves 1 and 2 either simultaneously or in sequence is three times as troublesome as operating a single valve. Also, the three valves take up three times as much installation space as a single valve.
The arrangement in which the single butterfly valve V is used is free of any of these problems. But this valve has a problem in that since the valve body 7 is turned to open and close the valve, a large housing is needed to turn the valve body. To open and close the valve with high accuracy, the valve body has to be turned by a predetermined angle very accurately. Water sealability by the pressure contact of the rotary valve body 7 against the valve seal is insufficient.
In the arrangement of FIG. 14, various techniques are known in which water pressure in the water main S is used to control the shutoff valves 1 and the on-off valve 2. One of these techniques is disclosed in registered Japanese utility model publication 3018335. Another similar conventional arrangement is shown in FIG. 16, which includes an emergency shutoff valve 1 and an on-off valve adapted to be opened in an emergency, each valve having two pilot valves 8 and 9.
The shutoff valve 1 is provided in a bypass line P and its return-to-normal and shutoff pilot valves 8 and 9 each comprise a diaphragm 8a, 9a, a spring 8b, 9b biasing the diaphragm 8a, 9a, a valve body 8c, 9c coupled to the diaphragm through a valve rod, and its valve seat 8d, 9d. In a normal situation, in which water main pressure is below a predetermined level, the water main pressure is applied to both pilot valves 8 and 9, so that the springs 8b, 9b are compressed by the diaphragms 8a, 9a, and the valve body 8c separates from the valve seat 8d, while the valve body 9c is pressed against the valve seat 9d, thus keeping the water main pressure from acting on the cylinder valve 1a of the emergency shutoff valve 1. In this state, the inner and outer pressures P1 and P2 satisfy the relation P1&gt;P2, so that the cylinder valve 1a separates from the valve seat 1c. The shutoff valve 1 thus opens.
If the water main pressure drops below the biasing force of the springs 8b and 9b due e.g. to an earthquake, as shown in FIG. 16B, the pilot valve body 8c of the pilot valve 8 is pressed against the valve seat 8d, while the valve body 9c of the pilot valve 9 separates from the valve seat 9d, under the force of the springs 8b and 9b, respectively. Water main pressure is thus applied in the cylinder 1b (P1.apprxeq.P2). The diameter D1 of the valve seat of the emergency shutoff valve 1 is smaller than the diameter D2 of the cylinder 11 (D1&lt;D2). Thus, in this state, the relation is met, so that the cylinder valve 1a is seated on the valve seat 1c, thus closing the pipe P.
The two pilot valves 8 and 9 used in this emergency water storage tank structure need a large installation space, make the arrangement of connecting pipes t complicated, increase the facility cost, and are more likely to fail.
In the conventional arrangement of FIG. 17, a three-way valve is used instead of the pilot valves 8, 9. This valve V has, as shown in the figure, a valve chest 100 having opposed first and second ports 101, 102, and a third port 103 between the ports 101 and 102. The edges of the openings of the ports 101 and 102 serve as first and second valve seats 101a and 102a on which a valve body 104 is adapted to be selectively seated by means of a valve rod 105 (as shown by solid and chain line in FIG. 17A) to change the flow direction by selectively communicating first port 101 with third port 103 or second port 102 with third port 103.
But in this three-way valve, when the valve body 104 separates from the first valve seat 101a or the second valve seat 102a, as shown in FIG. 17B, the valve body 104 communicates the third port 103 with both the first and second ports 101 and 102. Thus, if this three-way valve V is used as a pressure-responsive pilot valve, communication from the first port 101 to the ports 102 and 103 become unstable because no flow direction changeover is possible. This lowers the reliability of changeover operation. For example, in the above emergency water storage tank structure, a reliability problem arises because the changeover by the emergency shutoff valve 1 and the on-off valve 2 cannot be carried out reliably. Especially if the water pressure in the water main P changes slowly, or if its change stops near the changeover setting pressure, the above instability state is created.
Using two pilot valves 8, 9 needs adjustment of their set pressures. The adjustment therefor is troublesome and if there is anything wrong in the adjustment, no desired action will be possible. That is, if only the set pressure of the return-to-normal pilot valve 8 is too low, i.e. 4 kg/cm.sup.2 due to weak pressure of the spring 8b, in spite of the fact that the set pressures of both pilot valves 8, 9 have to be 5 kg/cm.sup.2, when pressure in the pipe P drops from a normal pressure to the set pressure (5 kg/cm.sup.2), the shutoff pilot valve 9 will operate normally (from close to open), thus supplying pressurized water in the pipe P into the cylinder 1b. But the return-to-normal pilot valve 8 does not operate (remains open) because the water pressure is still higher than its set pressure 4 kg/cm.sup.2. Thus, even when pressurized water is supplied, it is simply discharged. Thus, although the pressure in the cylinder 1b may rise a little, it will never rise to a predetermined pressure, so that the cylinder valve 1a cannot be seated on the valve seat 1c reliably, and since the shutoff valve 1 is not closed completely, upstream water will keep leaking to the downstream side of the valve 1.
At this time, the pressure in the cylinder 1b is determined by the difference between the supply and discharge pressures of pressurized water. Since the fluid pressure (water pressure) in the pipe P, flow rate, degree of opening of the valve (cylinder valve 1a), etc. change, the degree of opening of the valve and the like cannot be kept constant and tend to be unstable. The amount of leakage to the downstream side is also unstable. The pipelines are thus unstable. Such an unstable state may also occur if there is a difference in length between the connecting pipes t of both valves 8, 9. Thus, the set pressures of both valves 8, 9 have to be determined taking into account the length and leakage of the connecting pipes t. Such adjustments are troublesome.
On the other hand, if the set pressure of the shutoff pilot valve 8 is too low, e.g. 4 kg/cm.sup.2, even if the water pressure in the pipe P drops to 5 kg/cm.sup.2 and the return-to-normal pilot valve 8 is closed, the shutoff pilot valve 9 will remain inactive (closed) and no pressurized water is supplied into the cylinder 1b. In this case too, the shutoff valve 1 will not close but remain in an unstable open state.
In both these unstable states, the water pressure in the pipe P will further decrease to 4 kg/cm.sup.2. At this point, the return-to-normal pilot valve 8 or the shutoff pilot valve 9 is activated (opens). Pressurized water is thus entirely applied in the cylinder 1b, so that the shutoff valve 1 stabilizes and is closed reliably.
An object of this invention is to provide a four-port changeover valve for changing over the flow path of the water main and the bypass pipe by axially moving the valve rod.
A second object of the invention is to eliminate an unstable state in which the flow direction cannot be changed over due to flows in two directions.
A third object is to provide, in a flow changeover valve assembly in an emergency water storage tank facility, means that make it possible to change over the flow path by the pilot pressure.
A fourth object is the provision of a pilot valve which eliminates the need for correlation between the preset pressures, which does not need a long, complicated piping, and which is easy to adjust the pressure and is less liable to fail.